Method of impregnating coils



Aug. 18, 1931. J. T. GOFF METHOD OF IMPREGNATING COILS Filed Sept. 22, 1930 fflfllll ll/ll rlllllfflll/IIIIIlI/ll ATTORNEY Patented Aug. 18, 1931 UNITED STATES PATENT OFFICE JAMES '1. GOFF, 0F WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA METHOD OF IMPREGNATING COILS Application filed September 22, 1930. Serial No. 483,466.

My invention relates to methods of insulating electrical conductors and more particularly to methods of producing insulated coils.

The principal object of my invention is to provide an improved method of insulating electrical conductors, such as coils, which comprises impregnating fibrous or enameled insulated coils with thickened China wood oil and then heating to convert the oil into a gelled state.

Another object of my invention is to provide a process of insulating electrical conductors, such as coils, which comprises wrapping a cellulosic or fibrous material around the coils and impregnating the same with thickened China wood oil, under pressure, in a nonoxidizing atmosphere.

A further object of my invention is to provide a process of insulating coils or conductors which comprises wrapping cotton tape around the coils, removing the moisture and air, and then impregnating the same with a viscous thickened China wood oil in an atmosphere of carbon dioxide after which the thickened China wood oil is converted into the gelled state.

A still further object of my invention is to provide a method of producing an insulating material which comprises preheating raw China wood oil to thicken it, impregnating cellulosic material with the thickened oil and then heating to convert the oil into the gelled state at a temperature which is substantially below the decomposition point of the cellulosic insulation.

It has heretofore been the practice, in insulating electrical apparatus, such as coils, to first insulate a plurality of conductors or turns of the windings of a coil from each other by means of an insulating varnish or by fibrous insulation, such as cotton or asbestos.

In accordance with the usual practice of insulating coils in which the windings are comparatively large, such as the field coils of railway motors and relatively larger magnet coils, the conductors or windings are insulated from each other by a suitable fibrous insulation, such as asbestos or cotton tape. The windings or conductors are then assembled, and a strip of cotton tape is helically wound liquid gum such as asphalt, under pressure,

for the purpose of filling the spaces between the insulated coils. It is essential that the spaces be filled as completely as possible to provide means for conducting the heat from the coils and so that a film of suflicient thickness will be formed to resist moisture and chemicals, such as salt spray or acid fumes.

The cotton tape is removed, with the excess gum, and several layers of varnished cambric cloth are wrapped around the impregnated coils. A layer of cotton tape is then applied over the cambric cloth. After the coils and insulation are thus assembled, it is found necessary to apply several coatings of varnish to the insulated coil in order to produce a coil having a good appearance and also satisfactory moisture and chemical resistance.

In smaller wire-wound coils, such as magnet coils and some types of field coils, the windings are insulated from each other by enamel and fibrous material, or, a layer of enamel alone; the layer of windings being separated from each other by cotton tape or yarn. In preparing such coils, it has been the practice to wrap the coil with a layer of cotton tape. A layer of stripping tape is then applied to the coil, and the insulated coil is then treated with a liquid gum. After impregnation, the stripping tape is removed to clean the surface. The coil is then buffed, immersed in a varnish and baked. It is then necessary to repeat the bufiing operation after which it is sprayed several times and dried after each spraying operation.

In coils of certain types, it has also been the practice to assemble the insulated windings and immerse them in a varnish containing a volatile solvent. The coil is then baked, and varnished cambric cloth or mica tape is wrapped around the assembled coil and a final layer of cotton or asbestos tape applied. The assembled structure is then the varnish containing the volatile solvent, the coating being baked after each application.

The foregoing methods of insulating coils are expensive and time consuming and do not produce uniformly good results. Attempts have accordingly been made to apply fibrous insulation to the coils and then 1mpregnate it with China wood oil in the raw state and subsequently heating it to a temperature of about 200 C. to gell the China wood oil. Similar attempts have also been made to apply China wood oil to coils which were provided with a suitable enamel, and

to gell the oil by heating to a high temperature. In the case of the fibrous insulation, the heat necessary to gell the oil decomposed the cellulosie insulation, and the volatile vaporswhich were given oif prevented the gelling of the oil and rendered the insulation porous. When the conductors were provided with an insulating varnish, such as enamel, the previous method was also unsatisfactory because, when the China wood oil was applied and heated in the manner specified, the enamel had the tendency to peel off at the temperature necessary to gell the oil.

I have made the discovery that electric conductors, assembled in the form of coils or windings, either coated with an enamel or wrapped with fibrous material, may be satisfactorily insulated by an improved process which comprises removing the moisture from the coil and then coating the assembled enamel coils or impregnating the fibrous insulation of a coil with thickened China wood oil which is allowed to drain in a nonoxidizing atmosphere and is then converted to the gelled state by heating in air or in an inert atmosphere.

My invention will be better understood by reference to the accompanying drawings in which:

Figure 1 is a cross-sectional view of the impregnating apparatus, and

Fig. 2 is a similar view of a field coil for a railway motor.

Referring to Fig. 1 of the drawings, raw China wood oil is placed in storage tank 1,

and the coils 2, to be impregnated are placed in the impregnating tank 3 which is heated by any suitable means. I prefer to heat tank 3 by means of electric energy, although gas or internal heating means, such as coils through which a heating fluid may be circulated, may be utilized. In order to prevent the premature gelling of the oil in the storage tank, it may be found necessary to provide suitable means for cooling the oil, such as coils 21, through which a cooling fluid may be circulated. Suitable racks 4, are provided in tank 3, to hold the coils 2 in position during the impregnating process.

The tanks 1 and 3 are connected by means of a pipe 5, which is provided with a valve 6.

A vacuum pump 7 and a cylinder 8, containing carbon dioxide gas, are connected to the tank 3 by means of suitable pipes 10 and 9, respectively. The valve 13 may be opened when it is'desired to evacuate tank 3.

In practicing my invention, I first thicken the China wood oil by heating it in a vacuum or in air at temperatures of 160 to 190 for a period of from 4.- to 18 hours or until' the oil has almost gelled. While thickening the oil in this manner, it should be agitated in order to insure uniformity of composition, by some suitable means, such as, by blowing gas through the oil or by means of a mechanical stirrer. During this thickening process, it is essential that the temperature of the oil he kept below 200 C. so that the gelling stage will not be attained prematurely. When a mechanical agitator is utilized, a vacuum may be employed to remove any volatile products which would otherwise render the gelling of the oil ditficult. The thickened oil thus produced is placed in tank 1.

In preparing the coils to be impregnated, the windings are first assembled and insu lated. For example, Fig. 2 shows a field coil for railway motors comprising a plurality of windings assembled in two layers 16. The windings of the conductor are insulated from each other by asbestos insulation 17, and the layers are separated by a sheet of mica 18. The coils thus assembled, are first wrapped with three layers of varnished cambric cloth 19, and then with a layer of cotton tape 20.

In the case of smallercoils, such as magnet coils, the windings of the conductor are insulated from each other by fibrous insulation, enamel or both, and, as a rule, a layer of cotton is placed between the layers of windings. One or more layers of the cotton tape or varnished cambric are then wrapped around the coils.

The insulated coils are preferably air baked, at temperatures varying from 115 C. to 125 (1., fora period of 2 to 3 hours, or until all of the moisture is removed, after which they are placed in the tank 3 which is evacuated by means of the pump 7. The vacuum is maintained for a sufficient time to remove the air and any remaining moisture, a trace of moisture being suflicient to prevent the gelling of the oil. If desired, however, the entire baking operation may be performed in the tank 3. The valve 6 is then opened, and the coils in the tank 3 are completely covered with the thickened China wood oil for a period of 1 to 3 hours, depending upon the size of the coils and, if insulated, with the thickness of the fibrous insulation.

The valve 6 is now closed, the valve 11 opened, and a pressure of about 80 pounds carbon dioxide per square inch is maintained within the impregnation tank 3, until all voids in the apparatus arefilled, during which time the oil is maintained at approximately roomtemperature tofl prevent the "gelling of tank.

the oil in the tankl. The valve 6 is then opened the thickened China wood oil is forced ack into thetank 1, and the impreg nated coils are allowed to drain at a'tem perature' of approximately 125 to- 150 C. in an atmosphere of carbon dioxide. The opening of valve 6 reduces the pressure of carbon dioxide to 25 to 15 pounds er square inch, which is preferably maintainedduring the draining of the coils, althoughthey may be drained in air. B'y'draining the coils in the manner specified, however, a smoother sur face is provided than when they are drained in air. The time required for the excess amount of thickened China wood oil to drain from the coils will vary from v1 to 5 hours, depending u on the size, surface area and type ofwinding of the coils.

inally, the impregnated coils are baked at a temperature of approximately 150 for 6 to 20 hours in carbon dioxide or in air, until the oil has polymerized and oxidized or both, and an insoluble gell has been formed.

My improved process may be applied to insulating coils of many different types or may be applied to conductors insulated from each other and assembled together, the assembly being wrapped with insulation of various kinds, such as asbestos or fibrous material. For example, my process is especially suitable for the impregnation of transformer,

coils made of wire covered with cellulosic or other fibrous material.

It will, therefore, be understood that the term coil, as utilized in the specification and claims, refers not only to the windings of a single conductor but refers also to a plurality of insulated conductors lying adjacent to or in close relationship to each other.

The pressure of carbon dioxide will depend upon the safety limit of the impregnating Satisfactory results are obtained in the impregnating operation, when the concentrationof carbon dioxide is maintained at from 40 pounds to 80 pounds per square inch. When less than 40 pounds per square inch of carbon dioxide is employed, the pressure is too low to force the varnish into the i insulation, thereby causing uneven impregnation. However, a concentration of carbon dioxide of over 80 pounds per square inch is not objectionable; in fact, superior impregnation will be obtained in a shorter length of time by increasing the concentration of carbon dioxide. Other nonoxidizing gases, such as nitrogen or mixtures of nitrogen and carbon dioxide, may be utilized, in place of the carbon dioxide, to provide the necessary pressure to force the thickened oil into the coils during the impregnating process or, if desired, hydraulic pressure may be employed.

The time and temperature required for the gelling of China wood oil may be appreciably reduced when from .05% to 0.2% by weight of mercuric iodine or iodine are present in the oil.

By my improved method, a. film is procomposition products of cellulose, which de crease the dielectric strength of the insulation, are not formed, as is the case with ordinary impregnating 0115. Furthermore, a

sufiicient amount of the China wood oil may be applied, in one operation, to completely fill the same, whereas, inprevious practice, at least three operations were required to secure the desired amount of impregnation.

v Transformer coils which have been treated by my process and placed in service in the usual transformer oils, form less free acid and cause less 'sludgingthan-the gums which have previously'been'employed and have ahigher dielectric stren h between turns.

While I have disclosed my invention [in considerable detail and have mentioned specific temperatures and pressures, it will;

be understood thatthe examples shouldfbe construed as illustrative and not by way of limitation. For example, it may be desirable to color the China wood oil by employing an organic dye or a small quantity of gum, such as gilsonite, in order to give the China wood oil a black appearance. From 2% to 5%, by weight, of organic dye or gum is sufiicient to produce a satisfactory black color in the oil. In view of the numerous modifications which may be effected therein without de parting from the spirit and scope of my invention, it is desired that only such limitations shall be imposed-as are indicated in the appended claims.

I claim as my invention '1. The processof insulatinga coil which ture under the pressure of a non-oxidizing gas, removing the excess of China wood oil, draining in a nonoxidizing atmosphere and baking in air to gell-the oil.

4. The process of insulating a coil which comprises wrapping the coil with fibrous insulation, impregnating the wrapped coil with thickened China wood oil, removing the exatmosphere and baking in air to gell the oil.

In testimony whereof, I have hereunto subcess of China wood oil, draining a nonoxidizing atmosphere and baking in air to gell the oil.

5. The process of insulating a coil which comprises wrapping the coil with fibrous insulation, impregnating the wrapped coil with thickened China wood oil, removing the excess of China wood oil, draining in air at atmospheric pressure and baking in air to gell the oil. 7

6. The process of insulating coils which comprises treating the conductor insulation with thickened China wood oil under pressure of a nonoxidizing gas, permitting the China wood oil to drain from the conductors at an elevated temperature while still maintaining a nonoxidizing atmosphere, and completing the drying of the conductors in air.

7. The process of insulating coils which comprises treating the coils with thickened China wood oil in the presence of a substance containing iodine, under pressure of a nonoxidizing gas, permitting the China. wood oil to drain from the coils at an elevated temperature while still maintaining a nonoxidizing atmosphere and completing the drying of the coils at an elevated temperature.

8. The process of insulating coils which comprises wrapping fibrous material around the coils, placing the wrapped coils in a container in which a partial vacuum is maintain ed heating the conductors to expel moisture and air, forcing thickened China wood oil over the coils and maintaining the thickened China wood oil in contact with the coils under pressure of a nonoxidizing gas for a sufficient length of time to thoroughly impregnate the coils, removing the thickened China wood oil and draining the coils at an elevated temperature in an atmosphere of nonoxidizing gas.

9. The process of insulating a coil which comprise treating the coil with thickened China wood oil at room temperature under pressure of a nonoxidizing gas, removing the thickened China wood oil and draining at an elevated temperature in an atmosphere of nonoxidizing gas, and baking to gell the oil.

10. In the process of insulating a coil, the step which comprises impregnating the coil with thickened China wood oil containing an iodide.

11. In the process of insulating an electrical coil, the steps which comprise wrapping the coil with a fibrous material and impregnating the wrapped coil with thickened China wood oil in which iodine is present.

12. The process of insulating a coil which comprises wrapping the coil with fibrous insulation, impregnating the wrapped coil with thickened China wood oil containing a coloring agent, removing the excess of colored China wood oil, draining in a nonoxidizing scribed my ber, 1930.

name this 19th day of Septem- JAMES T. GOFF. 

